1. Field of the Invention
The present invention relates to a communication system using a radio apparatus. More particularly, the present invention relates to a communication system that can reduce a communication load on an information provider of various contents or data.
2. Description of the Related Art
Recently, various radio apparatuses such as a portable telephone are widely used not only for calls but also for various other communications. Such communications include, for example, a download of data such as music data and the like from a predetermined home page by using the Internet, reception of mail, and upload of picture data, such as a photograph taken by a user, to a home page of a dealer in order to produce a photograph album.
An example of such a communication system is the Japanese Laid Open Patent Application (JPA 2000-90039) that discloses “Music Distributing Method, Transmitting Apparatus And Method, And Reproducing Apparatus And Method”. In this communication system, a music server and a client are connected to the Internet. The client prepares a public key and a secret key based on an ID unique to the reproducing apparatus. The public key is sent to and registered in a server, and the secret key is stored in the reproducing apparatus. The client requests the server to distribute music data. The encryption based on the registered public key is performed on the music data fetched from a music database (DB). The encrypted music data is sent to the client, and stored in the reproducing apparatus. At a time of a reproduction, the music data is decoded and reproduced in accordance with the secret key stored in the reproducing apparatus. The music data stored in the reproducing apparatus is encrypted in accordance with the key prepared on the basis of the ID unique to the reproducing apparatus. Thus, the other reproducing apparatuses cannot reproduce the music data. This configuration enables a system for distributing music data to sufficiently protect the copyright of the music data to be distributed.
Also, Japanese Laid Open Patent Application (JP-A-Heisei, 10-150460) discloses “Radio Picture Communication System”. In this radio picture communication system, a video server opens various picture information stored therein as a common file onto a network. A terminal station sends a title of picture information, which it desires to receive, as control information to a radio control station by using a second radio communication path. The control radio station sends the title of the picture information included in the control information received from the terminal station, to a radio picture station, and then instructs to send this picture information to the terminal station. In response to this instruction, the radio picture station reads out the picture information corresponding to the instruction from the common file, and then sends the picture information to the terminal station by using the first radio communication path. Thus, the radio picture terminal can conveniently receive high quality picture information.
Moreover, Japanese Patent No. 2924865 discloses “Voice Mail System”. In this voice mail system, a server and one or more terminals are connected through a communication medium to each other. The serer manages a memory for storing a plurality of voice mail data as an identifiable file in a memory area assigned for each terminal. The server is provided with transmitting means and memory control means. The transmitting means, when receiving a mail request through the communication medium from the terminal, reads out the voice mail data from the memory area of the memory assigned to a terminal of its transmission source, and transmits to the terminal of the transmission source. The memory control means, when receiving a mail edition signal, insert or add the voice mail data in the mail edition signal to a position specified by the mail edition signal, in the memory area of the memory assigned to the terminal of the transmission source. This configuration allows for extremely effective communication in a communication network characterized by high costs and transmission speeds slower than that of a wire line, because the same voice mail data is not transmitted and received between the server and the same terminals multiple times.
FIG. 1 shows an example of the conventional communication system disclosed in Japanese Laid Open Patent Application (JPA 2000-90039), in which a portable telephone is used as a radio apparatus. In this communication system, a portable telephone 101 wirelessly communicates with a base station 102. The base station 102 is connected to a portable telephone network 103, and the portable telephone network 103 is connected to the Internet 104. A content server 105 for providing various contents is connected to the Internet 104. The portable telephone 101 can access the desirable content from server 105 through the portable telephone network 103 and the Internet 104. For the purpose of easy explanation, FIG. 1 shows one portable telephone 101, one base station 102 and one content server 105.
In this communication system, let us suppose that the content server 105 is a server that exclusively provides a service of downloading music data. When a new song of a popular singer or the like is sold or a hit song is produced, a large number of portable telephones 101 access the content server 105 dedicated to the music downloading operation. The content server 105 establishes a link to each of the portable telephones 101 accessing the server, and distributes the music data requested by each of them. Thus, if the accesses are concentrated on the particular content server 105, the data distribution rate per hour for each portable telephone 101 from the content server 105 becomes very small. As a result, the time it takes for each portable telephone 101 to download the music data becomes long. Hence, this results in high communication costs.
Conventionally, the above problem is solved by employing a structure of several servers alongside the content server 105 in order to distribute the load. Such structure causes the facility cost on the side of the content server 105 to be increased. Such a measure may be effective for a content server 105 having a high access frequency. However, if the accesses are temporarily concentrated on a server, the fact that the size of the facility depends on the access peak creates a problem related to efficient use of the communication system. Thus, the problem that the downloading of data in the case of load concentration requiring abnormally long time is still not solved in many content servers.
As mentioned above, the music distribution has been described as an example. However, there may be a case that an overload is temporarily induced on the server side when electronic mails are collectively distributed to the side of the portable telephones, or when personal information is distributed to the portable telephones under a predetermined condition. This results in a similar problem, induced even when the uploading operations are temporarily concentrated.